UC San Diego

Advancing Electro-Optical Minimally Invasive Microprobes for Chronic Interfacing With Deep Intrinsic Neural Circuits

by

Zhiwar Firooz Hassan

Master of Science in NanoEngineering (Medical Devices and Systems)University of California San Diego, 2022 Professor Donald Sirbuly, Chair

Worldwide, neurological diseases are the second most prevalent cause of death. In addition to the loss of life, neurological diseases also present public health and care access issues due to astronomical costs associated with treatment and follow-up care related to various side effects. To better understand and treat neurological diseases, scientists seek to build technologies that can stimulate and record cells on a neuronal level. This is particularly challenging when studying neurons, as researchers are unable to distinguish individual cell differences within the neuronal clusters by their activity. Since 2005, advancements in genetic modifications and optics have given scientists new lanes of research and therapy in neuroscience. For this purpose, scientists have successfully engineered probes with the ability to optically stimulate and electrically record neurons. However, they have found that these probes failed shortly after implantation due to immune system responses. To overcome these limitations, researchers have shown that scaling down the size of the microelectrodes to less than the Soma body of the neuron reduces failure rates and increases the life of probes. Building on their discoveries, in this thesis we study the electrical and mechanical properties of the electro-optical Flex probe (EO-Flex) with a smaller size than the Soma body and the intervention of the neuron system on the scale of a single neuron. The EO-Flex probe was designed, fabricated, and characterized in the Sirbuly Lab at the University of California San Diego by graduate student Spencer Ward Ph.D., with the study of the stability of the metal layer in the probes and their mechanical buckling force by graduate student Zhiwar Hassan M.S. candidate. Chapter 2 addresses the electrical properties and stability of utilized metals in coaxial layers of two different sets of platinum and iridium oxide fabricated probes. Chapter 3 determines the buckling mode of various probe lengths from 100 µm to 1mm and their ability to withstand the maximum force of insertion before failing.